Magnetic recording media comprising a non-magnetic support having provided thereon a magnetic layer containing ferromagnetic iron oxide particles or ferromagnetic alloy particles dispersed in binders are widely used as media of video tapes, audio tapes and the like.
In recent years, together with the strong demand for higher density recording in a magnetic recording medium, demands for higher vision image qualities, and higher sound qualities have increased. Therefore, it has been necessary that electromagnetic properties be improved, that is, particularly that C/N (carrier/noise ratio) be increased and that BN (bias noise) be decreased.
For the above purposes, the size of ferromagnetic particles must be reduced and the number of magnetic particles per unit volume must be increased. However, if the specific surface area of ferromagnetic particles is increased to increase the number of magnetic particles per unit volume, voids are formed on the surface of the ferromagnetic particles and the particle size is not actually so small as desired or the axis ratio (ratio of a short axis to long axis) becomes lower, whereby the above objects can not be fulfilled. In other words, there are some problems, in that if voids are formed, loss of magnetic susceptibility increases, and in that if the axis ratio of ferromagnetic particles becomes lower, magnetic orientation of magnetic particles is not carried out effectively upon preparing a magnetic recording medium.
Furthermore, as the size of ferromagnetic particles is reduced, print-through characteristics tend to deteriorated due to the increase of low coercive force components in the ferromagnetic particles, such that the resulting medium, ultimately, can not be used practically.
Also, if the size of the ferromagnetic particles is reduced, the light-transmission degree of a magnetic layer increases. In a video tape deck (VHS type, 8 mm type, and the like), the end of a tape is detected by a photosensor capable of detecting light having a wavelength of about 900 nm. Therefore, the light-transmission degree of a tape must be 10% or less to avoid mis-operations of the photosensor. Accordingly, when the size of ferromagnetic particles is reduced, it becomes necessary to add light-intercepting particles into a magnetic layer in a large amount, or to provide a thick backing layer or a light-intercepting layer.
However, when light-intercepting particles are added into a magnetic layer in a large amount, electromagnetic properties are deteriorated. When a backing coat layer or another light-intercepting layer is provided to intercept light, surface properties and electromagnetic properties are deteriorated by the orange peel of the backing layer caused by making the layer thick.
When the size of ferromagnetic particles is increased to improve print through characteristics, and the like, there is a problem in that head wear increases.